Ammonium Acetate Buffer (ammonium + acetate_buffer)

Distribution by Scientific Domains


Selected Abstracts


Analysis of tricyclic antidepressant drugs in plasma by means of solid-phase microextraction-liquid chromatography-mass spectrometry

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2007
Claudete Alves
Abstract Solid-phase microextraction coupled to liquid chromatography and mass spectrometry (SPME-LC-MS) was used to analyze tricyclic antidepressant drugs desipramine, imipramine, nortriptyline, amitriptyline, and clomipramine (internal standard) in plasma samples. SPME was performed by direct extraction on a PDMS/DVB (60 m) coated fiber, employing a stirring rate of 1200 rpm for 30 min, pH 11.0, and temperature of 30 C. Drug desorption was carried out by exposing the fiber to the liquid chromatography mobile phase for 20 min, using a labmade SPME-LC interface at 50 C. The main variables experimentally influencing LC-MS response were evaluated and mathematically modeled. A rational optimization with fewer experiments was achieved using a factorial design approach. The constructed empirical models were adjusted with 96,98% of explained deviation allowing an adequate data set comprehension. The chromatographic separation was realized using an RP-18 column (150 mm 2.1 mm, 5 m particles) and ammonium acetate buffer (0.01 mol/l, pH 5.50) : acetonitrile (50 : 50 v/v) as mobile phase. Low detection levels were achieved with electrospray interface (0.1 ng/ml). The developed method showed specificity, linearity, precision, and limit of quantification adequate to assay tricyclic antidepressant drugs in plasma. Copyright 2007 John Wiley & Sons, Ltd. [source]


Simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method for the quantification of lacidipine in human plasma

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2004
N. V. S. Ramakrishna
Abstract A simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method was developed and validated for the quantification of lacidipine in human plasma using its structural analogue, amlodipine, as internal standard (IS). The method involves a simple single-step liquid,liquid extraction with tert -butyl methyl ether. The analyte was chromatographed on an Xterra MS C18 reversed-phase chromatographic column by isocratic elution with 20 mM ammonium acetate buffer,acetonitrile (10 : 90, v/v; pH 6) and analyzed by mass spectrometry in the multiple reaction monitoring mode. The precursor to product ion transitions of m/z 456.4 , 354.4 and m/z 409.3 , 238.3 were used to measure the analyte and the I.S., respectively. The chromatographic run time was 1.5 min and the weighted (1/x2) calibration curves were linear over the range 0.1,25 ng ml,1. Lacidipine was sensitive to temperature in addition to light. The method was validated in terms of accuracy, precision, absolute recovery, freeze,thaw stability, bench-top stability and re-injection reproducibility. The limit of detection and lower limit of quantification in human plasma were 50 and 100 pg ml,1, respectively. The within- and between-batch accuracy and precision were found to be well within acceptable limits (<15%). The analyte was stable after three freeze,thaw cycles (deviation <15%). The average absolute recoveries of lacidipine and amlodipine (IS) from spiked plasma samples were 51.1 1.3 and 50.3 4.9%, respectively. The assay method described here could be applied to study the pharmacokinetics of lacidipine. Copyright 2004 John Wiley & Sons, Ltd. [source]


Effect of eluent on the ionization efficiency of flavonoids by ion spray, atmospheric pressure chemical ionization, and atmospheric pressure photoionization mass spectrometry

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2001
Jussi-Pekka Rauha
Abstract The effect of nine different eluent compositions on the ionization efficiency of five flavonoids was studied using ion spray (IS), atmospheric pressure chemical ionization (APCI), and the novel atmospheric pressure photoionization (APPI), in positive and negative ion modes. The eluent composition had a great effect on the ionization efficiency, and the optimal ionization conditions were achieved in positive ion IS and APCI using 0.4% formic acid (pH 2.3) as a buffer, and in negative ion IS and APCI using ammonium acetate buffer adjusted to pH 4.0. For APPI work, the eluent of choice appeared to be a mixture of organic solvent and 5 mM aqueous ammonium acetate. The limits of detection (LODs) were determined in scan mode for the analytes by liquid chromatography/mass spectrometry using IS, APCI and APPI interfaces. The results show that negative ion IS with an eluent system consisting of acidic ammonium acetate buffer provides the best conditions for detection of flavonoids in mass spectrometry mode, their LODs being between 0.8 and 13 M for an injection volume of 20 l. Copyright 2001 John Wiley & Sons, Ltd. [source]


Hypericum perforatum,Chemical profiling and quantitative results of St. John's Wort products by an improved high-performance liquid chromatography method

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2002
M. Ganzera
Abstract The analysis of flavonoids, naphthodianthrones, and the phloroglucinol derivative hyperforin in H. perforatum is described in this article. In a 35-min HPLC run nine major compounds could be identified and baseline separated in the methanolic plant extracts. For an optimum separation the mobile phase consisted of 10 mM ammonium acetate buffer (pH 5.0) and an acetonitrile/methanol mixture; a Synergi MAX-RP 80 column (C-12 material) was used as stationary phase. Detection was performed at 270 nm, and the identity of the compounds was confirmed in an LC-MS experiment. Commercial St. John's Wort products were analyzed and qualitative and quantitative results are discussed. 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:623,630, 2002 [source]


Development and validation of a reverse-phase liquid chromatographic method for assay and related substances of abacavir sulfate

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 1 2007
U. Seshachalam
Abstract A simple isocratic liquid chromatographic method was developed for the determination of abacavir from its related substances and assay for the first time. This method involves the usage of C18 (Intertsil octadecyl silane-3V, 150 mm4.6 mm, 5 ,m) column. The method was validated over the range of 0.002,0.1 mg/mL for chloro impurity, 0.005,0.1 mg/mL for amino impurity and pyrimidine impurity, and 0.005,0.2 mg/mL for abacavir. The mobile phase consists of a mixture of 10 mM ammonium acetate buffer and ACN in the ratio of 90 : 10. The flow rate was set at 1.0 mL/min with UV detection monitored at 214 nm. The drug substance was subjected to stress conditions of hydrolysis, oxidation, photolysis, and thermal degradation. The developed method was validated for linearity, range, precision, accuracy, and specificity. This method can be conveniently used in a quality control laboratory for routine analysis of both related substances and assay. [source]


Determination of aerobic-anaerobic metabolism-related compounds in a Chaoborus flavicans population by infusion ion trap mass spectrometry of extracts of individual larvae

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2006
Maria da Graa Gama Melo
In a daily migration, the aquatic larvae of Chaoborus flavicans (a phantom midge) alternate oxygen-saturated and anoxic lake strata. To investigate this cycle, larvae were collected at a natural environment, and acetate, propionate, pyruvate, lactate, glycerol, phosphate, maleate, succinate, glucose and citrate were determined. Each larva was homogenized with 200,L water and deproteinized with a spin-filter; 50,L aliquots were mixed with 50,L of a buffer containing 80,mM propylamine, 20,mM HCl and 0.06,mM 2,4-dihydroxybenzoic acid (internal standard) in methanol. The extracts were infused in an electrospray ionization ion-trap mass spectrometer. The limits of detection for the [M,H], peaks ranged from 2,M for pyruvate and lactate to 200,M for acetate and glycerol. The MS2 ion-trap spectra obtained at pH 7 (ammonium acetate buffer) were used to distinguish maleate (cis -2-butenedioic), which gave [M,CO2,H], (m/z 71), from fumarate (trans -2-butenedioic), which showed first a loss of water yielding an instable peak at m/z 97. The compounds involved in the aerobic-anaerobic adjustment of the metabolism were revealed by linear discriminant analysis. Acetate, citrate, glucose, maleate (which decreased during the daytime), and particularly succinate (which increased), showed the maximal discrimination power between the day- and night-time samples. Copyright 2006 John Wiley & Sons, Ltd. [source]


Sensitive and selective liquid chromatography,tandem mass spectrometry method for the determination of metoclopramide in human plasma: application to a bioequivalence study

BIOMEDICAL CHROMATOGRAPHY, Issue 9 2010
Jaswanth Kumar Inamadugu
Abstract A simple, sensitive and rapid method has been developed and validated for determination of the metoclopramide (MCP) in 100,,L human plasma. The analytical procedure involves a liquid,liquid extraction method using tramadol as an internal standard (IS). Chromatographic separation was carried out on a HyPURITY ADVANCE column using a mobile phase consisting of acetonitrile and 10,mm ammonium acetate buffer in the ratio of 80:20 (v/v) at a flow rate of 0.3,mL/min. The total run time of analysis was 2.5,min and elution of MCP and IS occurred at 0.9 and 1.3,min, respectively. A linear response function was established for the range of concentrations 0.53,42.07,ng/mL (r > 0.99). The intra- and inter-day precision values for MCP met the acceptance as per FDA guidelines. MCP was stable in a battery of stability studies viz., bench-top, auto-sampler and freeze,thaw cycles. The developed assay method was successfully applied to an oral bioequivalence study in humans. Copyright 2010 John Wiley & Sons, Ltd. [source]


Liquid chromatographic,tandem mass spectrometry assay for quantitation of a novel antidiabetic S002-853 in rat plasma and its application to pharmacokinetic study,

BIOMEDICAL CHROMATOGRAPHY, Issue 7 2010
N. Gautam
Abstract A sensitive and selective LC-MS/MS method has been developed and validated for the estimation of novel antidiabetic synthetic flavonoid S002-853 in rat plasma using centchroman as an internal standard. The method involves a simple two-step liquid,liquid extraction with diethyl ether. The analyte was chromatographed on a Pierce Spheri-5, guard cyano column (30 4.6,,mm i.d., 5,,m) with isocratic mobile phase consisting of methanol,ammonium acetate buffer (pH 4.6, 10,,mm; 90,:,10, v/v) at a flow rate of 0.75,,mL/min. The API 4000 triple-quadrupole LC,MS/MS system was operated under multiple reaction-monitoring mode. The ionization was performed by electrospray ionization technique in positive ion mode. The chromatographic run time was 6,,min and the weighted (1/x2) calibration curves were linear over the range 0.78,400,,ng/mL. The limit of detection and lower limit of quantification were 0.195 and 0.78,,ng/mL, respectively. The intra- and inter-batch accuracy (%bias) and precision (%RSD) were found to be less than 8.47 and 11.6% respectively. The average absolute recoveries of S002-853 and internal standard from spiked plasma samples were >90%. S002-853 was stable for 8,,h at ambient temperature, 4 weeks at ,60C and after three freeze,thaw cycles. The assay was successfully applied to determine the pharmacokinetic parameters in male Sprague,Dawley rats after an oral dose administration at 25,,mg/kg. Copyright 2009 John Wiley & Sons, Ltd. [source]


Development and validation of a sensitive LC-MS/MS method with electrospray ionization for quantitation of pramipexole in human plasma: application to a clinical pharmacokinetic study

BIOMEDICAL CHROMATOGRAPHY, Issue 2 2009
D. Vijaya Bharathi
Abstract A highly sensitive and specific LC-MS/MS method has been developed and validated for the estimation of pramipexole (PPX) with 500 L human plasma using memantine as an internal standard (IS). The API-4000 was operated under multiple-reaction monitoring mode (MRM) using the electrospray ionization technique. Solid-phase extraction was used to extract PPX and IS from human plasma. The resolution of peaks was achieved with 0.01 m ammonium acetate buffer (pH 4.4):acetonitrile (30:70, v/v) on a Discovery CN column. The total chromatographic run time was 3.0 min and the elution of PPX and IS occurred at approximately 2.32 and 2.52, respectively. The MS/MS ion transitions monitored were 212.10 , 153.10 for PPX and 180.20 , 107.30 for IS. The method was proved to be accurate and precise at linearity range of 20,3540 pg/mL with a correlation coefficient (r) of ,0.999. The intra- and inter-day precision and accuracy values found to be within the assay variability limits as per the FDA guidelines. The developed assay method was applied to a pharmacokinetic study in human volunteers following oral administration of 0.25 mg PPX tablet. Copyright 2008 John Wiley & Sons, Ltd. [source]


An HPLC method for the determination and pharmacokinetic study of lehmannine in rat plasma

BIOMEDICAL CHROMATOGRAPHY, Issue 10 2008
Gang Zhao
Abstract A high-performance liquid chromatographic (HPLC) method for determining lehmannine (LMN) in rat plasma was developed for application in the pharmacokinetics study. The plasma was deproteinized with acetonitrile that contained an internal standard and was separated from the aqueous layer by adding sodium chloride. The HPLC assay was carried out using a VP-ODS column at 40C. The mobile phase was acetonitrile,0.02 mol/L ammonium acetate buffer,triethylamine (35:65:0.04, v/v/v). The flow rate was 1.0 mL/min. The detection wavelength was set at 220 nm. The method was used to determine the concentration,time profiles of LMN in the plasma following oral administration or bolus injection of LMN aqueous solution. The pharmacokinetic parameters of LMN were calculated for the first time by Drug and Statistics 1.0 program. Copyright 2008 John Wiley & Sons, Ltd. [source]


Optimization and validation of RP-HPLC-UV method with solid-phase extraction for determination of buparvaquone in human and rabbit plasma: application to pharmacokinetic study

BIOMEDICAL CHROMATOGRAPHY, Issue 5 2008
Gantala Venkatesh
Abstract A simple, sensitive and specific reversed-phase high-performance liquid chromatographic method with UV detection at 251 nm was developed for quantitation of buparvaquone (BPQ) in human and rabbit plasma. The method utilizes 250 L of plasma and sample preparation involves protein precipitation followed by solid-phase extraction. The method was validated on a C18 column with mobile phase consisting of ammonium acetate buffer (0.02 m, pH 3.0) and acetonitrile in the ratio of 18:82 (v/v) at a flow rate of 1.1 mL/min. The calibration curves were linear (correlation coefficient ,0.998) in the selected range. The method is specific and sensitive with limit of quantitation of 50 ng/mL for BPQ. The validated method was found to be accurate and precise in the working calibration range. Stability studies were carried out at different storage conditions and BPQ was found to be stable. Partial validation studies were carried out using rabbit plasma and intra- and inter-day precision and accuracy were within 7%. This method is simple, reliable and can be routinely used for preclinical pharmacokinetic studies for BPQ. Copyright 2007 John Wiley & Sons, Ltd. [source]


Rapid quantification of lisinopril in human plasma by liquid chromatography/tandem mass spectrometry

BIOMEDICAL CHROMATOGRAPHY, Issue 4 2007
Weiwei Qin
Abstract An assay based on protein precipitation and liquid chromatography/tandem mass spectrometry (LC-MS/MS) has been developed and validated for the quantitative analysis of lisinopril in human plasma. After the addition of enalaprilat as internal standard (IS), plasma samples were prepared by one-step protein precipitation using perchloric acid followed by an isocratic elution with 10 mm ammonium acetate buffer (pH adjusted to 5.0 with acetic acid),methanol (70:30, v/v) on a Phenomenex Luna 5C18 (2) column. Detection was performed on a triple-quadrupole mass spectrometer utilizing an electrospray ionization (ESI) interface operating in positive ion and selected reaction monitoring (SRM) mode with the precursor to product ion transitions m/z 406,246 for lisinopril and m/z 349,206 for enalaprilat. Calibration curves of lisinopril in human plasma were linear (r = 0.9973,0.9998) over the concentration range 2,200 ng/mL with acceptable accuracy and precision. The limit of detection and lower limit of quantification in human plasma were 1 and 2 ng/mL, respectively. The validated LC-MS/MS method has been successfully applied to a preliminary pharmacokinetic study of lisinopril in Chinese healthy male volunteers. Copyright 2007 John Wiley & Sons, Ltd. [source]


Pharmacokinetic study of free-form sinomenine in rat skin by microdialysis coupled with liquid chromatography,electrospray mass spectrometry

BIOMEDICAL CHROMATOGRAPHY, Issue 1 2007
Hong Zheng
Abstract Sinomenine (7,8-didehydro-4-hydroxy-3,7-dimethoxy-17-methylmorphinan-6-one) is a pure alkaloid extracted from the Chinese medical plant. In this report a liquid chromatography,electrospray mass spectrometry (LC,ESI-MS) method with in vivo microdialysis for the pharmacokinetic study of free-form sinomenine in rat skin has been developed. A microdialysis probe was surgically implanted into the subcutaneous tissue of the rats and an isotonic phosphate buffer (PBS) was used as the perfusion medium. Samples were collected and then analyzed off-line by LC,ESI-MS. The chromatographic separation was achieved within 4.2 min by using a narrow-bore Xterra C18 column (2.1 150 mm, 5 m) with acetonitrile,(10 mmol/L ammonium acetate buffer, 0.1% acetic acid) (15:85, v/v). Ion signal m/z 330.1 for sinomenine was measured in the positive mode. Linearity was established for the range of concentrations of 2.0,10000.0 ng/mL with a coefficient of determination (r) of 0.9989. The intra- and inter-day reproducibility of the present method was better than 6%. The lower limit of quantification (LLOQ) was 1.0 ng/mL. The proposed method described provides more authentic information on pharmacokinetics and metabolism at the site of action by using the coupling of microdialysis to LC,ESI-MS technique than the traditional sampling methods. Copyright 2006 John Wiley & Sons, Ltd. [source]


Simultaneous determination of estramustine phosphate and its four metabolites in human plasma by liquid chromatography,ionspray mass spectrometry

BIOMEDICAL CHROMATOGRAPHY, Issue 5 2004
M. Breda
Abstract A sensitive and selective method, using liquid chromatography,ionspray mass spectrometry, was developed and validated for the simultaneous determination of Estracyt (estramustine phosphate) and its four metabolites, estramustine, estromustine, estrone and estradiol, in human plasma. Deuterated internal standards were available for all analytes. The ,ve compounds were extracted from plasma by protein precipitation with acetonitrile. The chromatographic separation was performed using a Zorbax SB C18, (150 4.6 mm i.d., 5 m) reversed-phase column under gradient conditions with a mobile phase containing 2 mm ammonium acetate buffer (pH 6.8) and acetonitrile. MS detection was by electrospray ionization with multiple reaction monitoring in the positive ion mode for estramustine phosphate, estromustine and estramustine, and in the negative ion mode for estrone and estradiol. The limit of quantitation was 10 ng/mL for estramustine phosphate, 3 ng/mL for estromustine, estramustine and estrone and 30 ng/mL for estradiol. Linearity was veri,ed from these LLOQs up to about 4000 ng/mL for the parent drug and 2000 ng/mL for the metabolites. Inter-day precision and accuracy values were all less than 15%. This assay was applied successfully to the routine analysis of human plasma samples collected in cancer patients administered estramustine phosphate intravenously. Copyright 2003 John Wiley & Sons, Ltd. [source]


Determination of lamivudine/stavudine/efavirenz in human serum using liquid chromatography/electrospray tandem mass spectrometry with ionization polarity switch

BIOMEDICAL CHROMATOGRAPHY, Issue 6 2002
Bin Fan
A high-performance liquid chromatography/tandem mass spectrometry (LC-MS-MS) method with ionization polarity switch was developed and validated in human serum for the determination of a lamivudine (3TC)/stavudine (d4T)/efavirenz combination HIV therapy. Solid phase extraction (SPE) was used to extract these anti-HIV drugs and internal standard aprobarbital. A gradient mobile phase consisting of acetonitrile and 20,mM ammonium acetate buffer with pH adjusted to 4.5 using glacial acetic acid was utilized to separate these drugs on a hexylsilane column (150,,2.0,mm i.d.). The total run time between injections was 18,min. The precursor and major product ions of these drugs were monitored on a triple quadrupole mass spectrometer in the multiple reactions monitoring (MRM) mode. Ionization polarity was switched in the middle of the LC run allowing these anti-HIV drugs with different physicochemical properties to be detected simultaneously. The effect of ion suppression from human serum was studied and no interference with the analysis was noted. The method was validated over the range of 1.1,540,ng/mL for 3TC, 12.5,6228,ng/mL for d4T and 1.0,519,ng/mL for efavirenz. The method was shown to be accurate, with intra-day and inter-day accuracy less than 14.0% and precise, with intra-day and inter-day precision less than 13.1%. The extraction recoveries of all analytes were higher than 90%. Copyright 2002 John Wiley & Sons, Ltd. [source]


An improved high-performance liquid chromatography method for quantification of methotrexate polyglutamates in red blood cells of children with juvenile idiopathic arthritis

BIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 3 2009
Hroch
Abstract Methotrexate is used widely in the pharmacotherapy of juvenile idiopathic arthritis. Polyglutamates of methotrexate are active metabolites which accumulate in cells including erythrocytes. Their intracellular concentration may reflect methotrexate bioavailability and, at the same time, may serve as a bioindicator for optimization of methotrexate therapy and drug monitoring. Therefore, a simple and selective isocratic reversed phase chromatographic method with fluorescence detection (excitation/emission wavelengths of 370/463,nm) was developed which quantifies the sum of all methotrexate polyglutamates in erythrocytes as methotrexate after their enzymatic conversion with ,-glutamylhydrolase. Separation was carried out on a Phenomenex GEMINI C18 column using a mobile phase flowing at a rate of 0.6,ml/min and consisting of a mixture (110:890:0.25 v/v) of acetonitrile, ammonium acetate buffer (0.05,m, pH=5.5) and hydrogen peroxide 30% (w/w). The method was found linear over the concentration range of 25,400,nmol/l. Its intra- and inter-day precision and accuracy were characterized by coefficients of variation and relative errors less than 20%. The limits of detection and quantification achieved 10.9 and 32.9,nmol/l, respectively. The method was proved suitable for monitoring the concentration of methotrexate polyglutamates in erythrocytes of patients with juvenile idiopathic arthritis. Copyright 2009 John Wiley & Sons, Ltd. [source]